Efficiency Of Cathodic Protection Research Articles

Effect of barnacle on the cathodic protection of high-strength steel and its potential risk related to hydrogen permeation

The cathodic protection efficiency and hydrogen permeation behaviour of high-strength steel with barnacle adhesion in the tidal zone were studied using field exposure and laboratory simulation tests for 2 years. Because of the shielding effect, barnacles can lead to an uneven calcareous deposition, a flatter morphology and a higher protection efficiency of steel. By contrast, because of the higher hydrogen permeation current at the edge of the barnacle adhesion area (caused by a higher hydrogen evolution rate), barnacle adhesion can promote hydrogen permeation. A mechanism was proposed to explain the observed phenomenon, and its effect on service safety was analysed.

Comparison of the Cathodic Protection of Epoxy Resin Coating/Zinc-Rich Coatings on Defective Areas under Atmospheric and Immersion Conditions: The Secondary Activation of Zinc Particles

The cathodic protection provided by epoxy coating/epoxy zinc-rich coatings on defective areas under atmospheric and immersion conditions was studied via a Q235 wire beam electrode (WBE), scanning electron microscopy, X-ray diffraction, and surface morphology analysis. The results showed that the cathodic protection processes under the two test conditions displayed significant differences. The effective protection time of the defective area under the atmospheric condition was 1.7 times that under the immersion condition. Compared with the immersion condition, zinc particles in zinc-rich coatings under the atmospheric condition exhibited higher cathodic protection efficiency. The possible activation mechanism of zinc particles under the two conditions was elucidated.

Effect of outer rust layer on cathodic protection and corrosion behavior of high-strength wire hangers with sheath crack in marine rainfall environment

After the high-density polyethylene (HDPE) sheath crack, the hanger steel wires of large-span suspension bridge are prone to corrosion under the erosion of the marine rainfall environment. This study investigates the influence of the outer rust layer on the impressed current cathodic protection (ICCP) and the corrosion behavior of hanger steel wires. The corrosion morphology and corrosion products of the wire are analyzed by SEM and XRD. The result shows that in the simulated marine rainfall environment, both ICCP and removal of the outer rust layer can reduce the corrosion rate of hanger steel wires. Especially the removal of the outer rust layer can significantly improve the cathodic protection efficiency. Removing the initial outer rust layer on the surface before applying ICCP is a benefit for forming a complete and dense corrosion product layer. In addition, it contributes to the generation of Zn5(OH)8Cl2H2O and Al2O3 with stable structures in the corrosion products. These corrosion products benefit to forming a passivation film, which helps isolate the iron matrix from harmful substances.

Assessing coating integrity and cathodic protection on buried pipelines under horizontal directional drilling conditions

ABSTRACT A moving electrochemical probe technique is developed for probing coating damages on underground pipelines installed by horizontal directional drilling (HDD) and for assessing the efficiency of cathodic protection (CP) through measuring local polarisation currents and local electrochemical impedance spectroscopy (EIS). The capability and accuracy of the probe in detecting coating defects have been evaluated, and compared with current techniques, using a simulated HDD pipe in a borehole. Results show that the probe is able to detect the locations of coating defects over the HDD pipe and that the capacitance of coating defects calculated from EIS data is a rather accurate parameter for defect size determination. The probe has also been used to apply local CP over coating defects for enhancing local corrosion protection. Preliminary field testing on a section of simulated HDD pipe has also shown reasonable accuracy of the probe in determining coating defect locations and sizes.

Cathodic Protection of Complex Carbon Steel Structures in Seawater

Cathodic protection efficiency of complex carbon steel structures in confined seawater environment was studied using a specific experimental device. Schematically, this device consisted of a Plexiglas matrix, crossed by a channel 50 cm long, 5 mm deep, 1.5 to 5 cm wide, which moreover included four bends at 90°. Seawater flowed continuously inside the channel over 12 steel coupons embedded in the Plexiglas matrix. Cathodic protection was applied at a constant potential of −1060 mV vs. Ag/AgCl-seawater with respect to a reference electrode located outside the channel, at the seawater flow entry. The potential of four selected coupons was monitored over time via a microelectrode set close to each coupon. It varied significantly with the distance separating the coupons from the channel entry. At the end of the 3.5-month experiment, a polarization curve was acquired. The residual corrosion rate under cathodic protection was estimated via the extrapolation of the anodic Tafel line. It varied from <1 µm yr−1 to 16 µm yr−1, depending on the potential reached by the coupon (between −900 and −1040 mV vs. Ag/AgCl-seawater) at the end of the experiment and on the properties of the calcareous deposit formed on the steel surface.

Investigation on efficiency of cathodic protection applied on steel in concrete cylinder with CFRP wrap serving as anode

The combination of strengthening and corrosion protection by using multi-functional material is an attractive topic recently. In this paper, carbon fiber reinforced polymer (CFRP) was utilized as a repair material and an anode of impressed current cathodic protection (ICCP) owing to its excellent mechanical and electrochemical properties. The effects of protection methods (non-protection, epoxy coating, CFRP wrapping, CFRP wrapping and ICCP), pre-corrosion degrees (3 %, 6 %, and 12 %), and ICCP current densities (5, 20, and 80 mA/m2) on corrosion performance of reinforced concrete (RC) cylinders were investigated by means of electrochemical measurements. The results showed that the double protection provided by CFRP wrapping and ICCP worked much better than the sole epoxy coating or the sole CFRP wrapping when an appropriate current density was applied. The optimal ICCP current density depended on the pre-corrosion severity of RC specimen. A current density of 20 mA/m2 resulted in the greatest improvements in charge transfer resistance for the 6 % and 12 % pre-corroded specimens while the optimal current density was 5 mA/m2 for the 3 % pre-corroded specimen. Moreover, CFRP wrapping led to greater increases in charge transfer resistance than epoxy coating. It suggested that, besides the contribution of epoxy to isolate harmful substances, confinement provided by CFRP wrapping may benefit corrosion alleviation in a further step by densifying the core concrete and consequently impeding ion transport and oxygen availability. This work provides a basis for further optimization design of ICCP-strengthening technique applied on corroded RC components to achieve higher efficiency.

Effect of current density on the cathodic protection efficiency and mechanical properties of pre-stressed high-strength steel wires for stay cable

Stay cables are the main force-bearing structures of cable-stayed bridges, which are mainly composed of internal high-strength steel wires and external high-density polyethylene (HDPE) sheaths. When the external HDPE sheaths crack, the internal high-strength steel wires are severely corroded, thereby endangering the security of the whole bridge. The effects of pre-stress level and protection current density on the cathodic protection efficiency and mechanical properties of stay cable high-strength steel wires were investigated in this study on the basis of the impressed current cathodic protection (ICCP) method for stay cable high-strength steel wires in rainwater environment. The corrosion degree of steel wires was characterized qualitatively and quantitatively by observing the macro and micro morphologies of the corrosion specimen and the weight loss measurement. The ICCP efficiency was evaluated in terms of the variation of open circuit potential (OCP) and instant-off potential (IOP). Static tensile test was used to investigate the difference in the mechanical properties of steel wires with different corrosion degrees. Results showed that the corrosion rate of steel wires increased with pre-stress level, and the greater the pre-stress, the higher the corrosion probability of steel wires. The application of ICCP reduced the accumulation of rust on the surface of the steel wires and the number and size of corrosion pits. The ICCP efficiency increased with the protection current density. No significant difference was found in the IOP values of the steel wires with different pre-stress levels when the protection current density was constant. All the steel wires with ICCP in the later stage of the test were effectively protected and are not in the overprotected state.

Методика определения поляризационного потенциала при проведении коррозионных обследований подземных трубопроводов

Values of metal potentials, which exceed or equal to the potential at which the corrosion rate of the metal does not exceed 0.01 mm/year, in international practice, are a condition for the effectiveness of cathodic protection of underground pipelines. It is called polarization potential. The range of polarization potentials, which correspond to effective corrosion protection, was determined experimentally as a result of a large number of field tests in different operating conditions. The values of polarization potentials can vary from minus 0.65 V to minus 1.15 V, measured relative to copper sulfate electrode (C.S.E). There are cases during corrosion surveys of underground pipelines, when the measured values of polarization potentials with the help of measuring instruments, intended for this purpose, significantly exceed the maximum permissible value. The author offers an original method for determining the polarization potential based on the analysis of the dependence of the auxiliary electrode potential on the time after the interruption of the polarization current. The values of polarization potentials obtained using this technique are in the standard range. The method can be recommended for experimental use in corrosion surveys of underground pipelines in various operating conditions in order to confirm the compliance of the obtained results with the condition of cathodic protection efficiency.

UNDERGROUND PIPELINE CORROSION MONITORING SYSTEM

One of the pressing issues of underground gas and oil pipelines protection against corrosion is the reliability of the cathodic protection efficiency assessment. This work is devoted to the problem of insulation coating transient resistance control and the effectiveness of underground structure protection by its potential. The assessment of the decrease in the protected structure potential due to the inclusion of potential sensors that are part of the stationary copper-sulfate comparison electrodes in the cathodic protection scheme in the absence of measurements is performed. Recommendations on documentary standard correction are presented. It is necessary to reconsider the approach to measuring potentials, abandon the excessive use of sensors due to their inefficiency, optimize the placement of diagnostic points using remote monitoring methods based on the introduction of world experience in applying the electrochemical impedance spectroscopy method and technical and economic feasibility.

An Array of Multielectrodes for Locating, Visualizing, and Quantifying Stray Current Corrosion

An array of multielectrode corrosion probes, designed based on a series of coupled wire beam electrodes (WBEs), has been devised as a new tool for locating, visualizing, and quantifying the effects of stray currents on buried pipeline corrosion. It has been demonstrated in laboratory simulation experiments that this WBE probe array is capable of detecting stray current corrosion affected sites along a pipeline, visualizing stray current corrosion patterns and corrosion rates, and evaluating the efficiency of cathodic protection against stray current corrosion. Based on these results, two applications of this WBE probe array have been proposed for stray current corrosion survey and monitoring.

Cathodic protection in reinforced concrete structures affected by macrocell corrosion: a discussion about the significance of the protection criteria

Cathodic protection is a technique that has been used to control corrosion and increase the service life of reinforced concrete structure. Standards as EN ISO 12696 give protection criteria for both impressed current and sacrificial anodes techniques, based on potential value or decay during a depolarization sequence. The polarization (current ON) and depolarization (current OFF) is experimentally studied on a corroded concrete wall thanks to six references electrodes and compared to a time-dependent modelling using FEM software COMSOL Multiphysics. Both experimental and numerical results show significant differences in the time response according to electrode location. This conclusion indicates that the concept of protection criteria defined by the standards is not suitable to assess the efficiency of cathodic protection applied to reinforced concrete structure.

Effects of Carbon Nanotube-Carbon Fiber Cementitious Conductive Anode for Cathodic Protection of Reinforced Concrete

Abstract Carbon nanotube-carbon fiber/cement-based composites used as auxiliary anode for cathodic protection of reinforced concrete were explored in this paper. Cathodic protection was applied with impressed current and its efficiency was verified by corrosion potential, corrosion current, and AC impedance spectroscopy. Results showed that cement composites containing 0.4 wt. % carbon fiber and 0.5 wt. % carbon nanotubes exhibit the optimum electrical and mechanical properties. Effective protection on steel re-bars can be expected due to a sufficient negative potential shift by the applied electric current. Compared with a carbon fiber cementitious conductive anode system, a decrease of corrosion current of steel re-bars was observed for the carbon nanotube-carbon fiber cementitious conductive anode system. During cathodic protection, both capacitive loop radius of a Nyquist plot in the intermediate frequency region and the charge transfer resistance increased with time. A detailed mechanism analysis of the efficiency of cathodic protection using the carbon nanotube-carbon fiber cementitious conductive anode is also included.

Monitoring cathodic protection of buried pipeline by means of a potential probe with an embedded zinc reference electrode

According to international standard, cathodic protection efficiency is controlled by monitoring IR-free potential. Nowadays commercial probes are available to perform correct potential reading, eliminating the ohmic drop contribution. In this paper, a new probe with a zinc reference electrode embedded in a proper backfill is proposed. Zinc is a promising material due to the low overvoltage in active condition and the high exchange current density. Laboratory tests were performed to select a stable backfill, in order to avoid any risk of shrinkage and mass loss. Sixteen mixtures based on gypsum, clay and other additives were considered. Gypsum, specifically sulfate ions, were used to maintain zinc in active condition; bentonite, absorbing humidity from the surrounding soil, guarantee a constant proper level of water content. Four additives, pure cellulose, an air-entraining agent, expanded glass granules and silica-based sand, were added to study the effect on water absorption, mass loss and electrical conductivity. Two of them were selected to prepare two probe prototypes with incorporated zinc electrode in order to verify the stability of both backfill and zinc during continuous cathodic protection monitoring.

Influence of different ways of chloride contamination on the efficiency of cathodic protection applied on structural reinforced concrete elements

Cathodic protection is a method to protect reinforced concrete structures located in saline environments against corrosion effect produced by Cl− penetration. But there are significant differences among these aggressive environments. The aim of this article is to show how different ways of saline contamination can affect the efficiency of cathodic protection. For this research, a series of laboratory specimens representing structural elements were subjected to two versions of cathodic protection (cathodic protection strictly speaking, and cathodic prevention), while two different ways of saline contamination were applied (permanent immersion in a NaCl solution and periodic pouring of discrete amounts of a NaCl solution in atmospheric exposure). Depending on the saline environment, differences in the efficiency of cathodic protection were detected. Results can be useful to determine the specific features of the cathodic protection to be applied in each case, taking into account both the initial Cl− content of the structural element and the particular saline environment where it is located.

Visualising dynamic passivation and localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients

A new method of visualising dynamically changing electrode processes has been demonstrated by mapping localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients. Dynamically shifting external electrical interferences such as anodic transients are known to affect the efficiency of cathodic protection (CP) of underground pipelines; however unfortunately conventional techniques including electrochemical methods have difficulties in measuring such effects. In this paper we report that the wire beam electrode has necessary temporal and spatial resolutions required for measuring and visualising the dynamic effects of anodic transients on CP, passivation and localised corrosion processes occurring on buried steel surfaces. For the first time a critical anodic transient duration has been observed and explained as the incubation period for the breakdown of passivity and the initiation of localised corrosion.

Effect of RuCl3Concentration on the Lifespan of Insoluble Anode for Cathodic Protection on PCCP

Prestressed Concrete steel Cylinder Pipe (PCCP) is extensively used as seawater pipes for cooling in nuclear power plants. The internal surface of PCCP is exposed to seawater, while the external surface is in direct contact with underground soil. Therefore, materials and strategies that would reduce the corrosion of its cylindrical steel body and external steel wiring need to be employed. To prevent against the failure of PCCP, operators provided a cathodic protection to the pre-stressing wires. The efficiency of cathodic protection is governed by the anodic performance of the system. A mixed metal oxide (MMO) electrode was developed to meet criteria of low over potential and high corrosion resistance. Increasing coating cycles improved the performance of the anode, but cycling should be minimized due to high materials cost. In this work, the effects of RuCl3 concentration on the electrochemical properties and lifespan of MMO anode were evaluated. With increasing concentration of RuCl3, the oxygen evolution potential lowered and polarization resistance were also reduced but demonstrated an increase in passive current density and oxygen evolution current density. To improve the electrochemical properties of the MMO anode, RuCl3 concentration was increased. As a result, the number of required coating cycles were reduced substantially and the MMO anode achieved an excellent lifespan of over 80 years. Thus, we concluded that the relationship between RuCl3 concentration and coating cycles can be summarized as follows: No. of coating cycle = 0.48*[RuCl3 concentration, M] -0.97 .

An overview of major methods for inspecting and monitoring external corrosion of on-shore transportation pipelines

Corrosion can occur on underground pipelines especially at coating defects, where metal can be considered directly exposed to the soil, or under disbonded coatings, where the occluded geometry significantly affects the efficiency of cathodic protection (CP). In order to ensure the effectiveness of corrosion mitigation measures such as CP and protective coatings, inspection and monitoring of pipeline corrosion are required. This paper provides an overview of major methods that are used for inspecting and monitoring external corrosion of on-shore pipelines subjected to CP. Particular focus is on discussing the advantages and limitations of major inspection tools that are used to ensure pipeline integrity, and electrochemical corrosion sensors that are designed to monitor pipeline corrosion processes and rates. It is shown that there is a need for expanding the capabilities of corrosion monitoring methods suitable for the pipeline industry.

외면부식 직접평가법 개발 및 국내 도입 연구

Abstract - To minimize the risk of corrosion on buried pipeline and to maximize the efficiency of cathodic protection, various indirect inspection techniques have been used for decades. In the United States, 49 CFR has regulated the external corrosion direct assessment for buried pipelines. In Korea, there is no provision for external corrosion direct assessment but there is only, according to the KGS Code, provision that if the survey of the defects of buried pipeline and the leakage test for the pipe were conducted, it is deemed to leakage inspection. We, therefore, have suggested external corrosion direct assessment method appropriate to domestic status through the survey of the regulations and standards of UK and the USA and the investigation of domestic situation on coating damage detection method. The proposed external corrosion direct evaluation method was used as the basis when introducing the precision safety diagnosis regulation for the medium-pressure pipe in Korea.Key words : external corrosion direct assessment, buried gas pipelines, coating defects

A Non-polluting Option Using Cathodic Protection for Hydrostatic Testing of Petroleum Tanks with Seawater

Oil storage tanks and derivatives must be evaluated by hydrostatic testing for leaks in sideways welds, possible cracks and failures that may have occurred during construction. Also in this test are observed defects and cracks in the concrete foundations that support the tank on the ground. The use of seawater as a fluid for hydrostatic testing in storage tank is economically attractive when the storage tanks are located near the sea. Due to its corrosive nature, seawater can cause damage to the internal surface of storage tanks. Generally, corrosion inhibitors and biocides are added to seawater in order to keep the corrosion rate under control. The disposal of water used in hydrostatic testing can represent an environmental problem whereas most corrosion inhibitors are toxic. Hydrostatic tests were run on bench scale tanks to investigate the efficiency of cathodic protection. These tests indicated that an aluminum anode (sacrificial anode) can efficiently replace corrosion inhibitors in storage tanks with the advantage that this corrosion protection system is not hazardous to the environment, as corrosion inhibitors can eventually be. The fixing of anodes in rubber floats and tubular modules represent a major innovation in the inner protection of tanks during the hydrostatic test with sea water.

Detecting the Efficiency of Cathodic Protection in Reinforced Concrete by Use of Galvanostatic Pulse Technique

The galvanostatic pulse technique has been applied in detecting the efficiency of cathodic protection in reinforced concrete based on the investigation on the response of galvanostatic pulse to the corrosion state of steel and perturbation magnitude of signal. Two data analysis methods were introduced to determine the corrosion rate. It is shown that the selection of perturbation magnitude of signal to be applied depends strongly on the corrosion state of steel. Too small current makes it difficult to separate the potential signal from background noise, whereas higher current results in intensive polarization. Thus, neither of two is beneficial for the data processing. The corrosion rate values obtained from chronopotentiometry method are on the low side during cathodic protection monitored by higher perturbation signal and correction of data employing polarization conversion method is suggested.